The present disclosure relates to an optical scanning device including a scanning lens which performs, on a surface to be scanned, imaging of a light beam that was deflected and scanned, and an image forming apparatus using the foregoing optical scanning device.
For example, a general optical scanning device that is used, for example, in laser printers and copiers includes a light source which emits a laser beam, a polygon mirror which reflects and deflects/scans the laser beam, and a scanning lens which performs imaging of the laser beam deflected for scanning on a peripheral surface (surface to be scanned) of a photoreceptor drum. As the scanning lens, a lens having a distortion (fθ characteristics) in which the angle of the incident light and the height of the image become a proportional relation is used. Moreover, the foregoing scanning lens is generally manufactured by molding a resin material in a metal mold.
One of the optical properties that are demanded in this kind of optical scanning device is that the field curvature is favorably corrected and the spot diameter of the beam generated by the laser beam is aligned across the entire image height. As conventional technology, known is technology which inhibits changes in the spot diameter by causing the curvature of the scanning lens in the sub scanning direction to continuously change from on axis toward off axis, and inverting the symbol of the curvature from on axis toward off axis. For example, a lens that has a meniscus shape on axis and a shape in which both surfaces are convex off axis is used as the scanning lens.
Nevertheless, the scanning lens of the foregoing conventional technology has a problem in that it is difficult to produce. In other words, upon processing the mold of the foregoing scanning lens, it is necessary to create a shape that will invert the symbol of the curvature in the sub scanning direction from on axis toward off axis. With this kind of inverted part of the curvature symbol, a discontinuous section tends to arise on the mold surface. Accordingly, a great difficulty is encountered in the die machining.
An object of the present disclosure is to provide an optical scanning device including a scanning lens in which the die machining thereof is easy and which yields superior optical performance, as well as an image forming apparatus using such an optical scanning device.